Commit 4d2bff5e authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds
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ipc: introduce obtaining a lockless ipc object 



Through ipc_lock() and therefore ipc_lock_check() we currently return the
locked ipc object.  This is not necessary for all situations and can,
therefore, cause unnecessary ipc lock contention.

Introduce analogous ipc_obtain_object() and ipc_obtain_object_check()
functions that only lookup and return the ipc object.

Both these functions must be called within the RCU read critical section.

[akpm@linux-foundation.org: propagate the ipc_obtain_object() errno from ipc_lock()]
Signed-off-by: default avatarDavidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Reviewed-by: default avatarChegu Vinod <chegu_vinod@hp.com>
Acked-by: default avatarMichel Lespinasse <walken@google.com>
Cc: Emmanuel Benisty <benisty.e@gmail.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7bb4deff

ipc/util.c

+57 −14
Original line number Diff line number Diff line
@@ -668,6 +668,28 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out) 
	out->seq	= in->seq;

}



/**

 * ipc_obtain_object

 * @ids: ipc identifier set

 * @id: ipc id to look for

 *

 * Look for an id in the ipc ids idr and return associated ipc object.

 *

 * Call inside the RCU critical section.

 * The ipc object is *not* locked on exit.

 */

struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id)

{

	struct kern_ipc_perm *out;

	int lid = ipcid_to_idx(id);



	out = idr_find(&ids->ipcs_idr, lid);

	if (!out)

		return ERR_PTR(-EINVAL);



	return out;

}



/**

 * ipc_lock - Lock an ipc structure without rw_mutex held

 * @ids: IPC identifier set
@@ -675,32 +697,53 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out) 
 *

 * Look for an id in the ipc ids idr and lock the associated ipc object.

 *

 * The ipc object is locked on exit.

 * The ipc object is locked on successful exit.

 */



struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)

{

	struct kern_ipc_perm *out;

	int lid = ipcid_to_idx(id);



	rcu_read_lock();

	out = idr_find(&ids->ipcs_idr, lid);

	if (out == NULL) {

		rcu_read_unlock();

		return ERR_PTR(-EINVAL);

	}

	out = ipc_obtain_object(ids, id);

	if (IS_ERR(out))

		goto err1;



	spin_lock(&out->lock);



	/* ipc_rmid() may have already freed the ID while ipc_lock

	 * was spinning: here verify that the structure is still valid

	 */

	if (out->deleted) {

	if (!out->deleted)

		return out;



	spin_unlock(&out->lock);

	out = ERR_PTR(-EINVAL);

err1:

	rcu_read_unlock();

		return ERR_PTR(-EINVAL);

	return out;

}



/**

 * ipc_obtain_object_check

 * @ids: ipc identifier set

 * @id: ipc id to look for

 *

 * Similar to ipc_obtain_object() but also checks

 * the ipc object reference counter.

 *

 * Call inside the RCU critical section.

 * The ipc object is *not* locked on exit.

 */

struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id)

{

	struct kern_ipc_perm *out = ipc_obtain_object(ids, id);



	if (IS_ERR(out))

		goto out;



	if (ipc_checkid(out, id))

		return ERR_PTR(-EIDRM);

out:

	return out;

}

ipc/util.h

+2 −0
Original line number Diff line number Diff line
@@ -123,6 +123,7 @@ void ipc_rcu_getref(void *ptr); 
void ipc_rcu_putref(void *ptr);



struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int);

struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id);



void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out);

void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out);
@@ -168,6 +169,7 @@ static inline void ipc_unlock(struct kern_ipc_perm *perm) 
}



struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids, int id);

struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id);

int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,

			struct ipc_ops *ops, struct ipc_params *params);

void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,

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